Question 1

What does P0171 mean?

Accepted Answer

P0171 - System Too Lean (Bank 1). The engine is running too lean on bank 1 — too much air or not enough fuel. The PCM has maxed out its fuel trim adjustments. This is one of the most common check engine light codes.

Question 2

What are the symptoms of P0171?

Accepted Answer

Check engine light, Rough idle, Hesitation on acceleration, Poor fuel economy, Possible misfires at idle, Hissing sound from engine bay

Question 3

What causes P0171?

Accepted Answer

Vacuum leak (intake gasket, brake booster hose, PCV valve), Dirty or failed MAF sensor, Weak fuel pump, Clogged fuel filter, Leaking fuel injector O-ring, Cracked intake boot, Exhaust leak before O2 sensor

Question 4

How much does it cost to fix P0171?

Accepted Answer

Typical repair cost: $50-$800. Check fuel trims with a scan tool. If LTFT is +15% or higher at idle but drops at higher RPM, it's almost certainly a vacuum leak. If LTFT stays high at all RPMs, suspect fuel delivery. Clean the MAF sensor first — free and fixes this ~30% of the time.

P0171 — System Too Lean (Bank 1)

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Common symptoms of P0171

Common causes of P0171

Repair cost & difficulty

Vehicles commonly affected

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